Bunuel wrote:

What is the sum of the digits of integer x, where \(x = 4^{10} * 5^{13}\)?

(A) 13

(B) 11

(C) 10

(D) 8

(E) 5

Answer is B as follows

\(x = 4^{10} * 5^{13} = 2^{20}*5^{13} = 10^{13}*2^7 = 10^{13}*128\)

Sum of the digits = 1+2+8 = 11

Hence B

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